Why do you think that? It seems needlessly complex to me when you could just have a simple permission pop up in the web app. What's the benefit of downloading an executable?
Besides the permissions stuff giving a single browser window access to raw usb data seems also technically wrong. There are lots of reasons why we now have drivers instead of applications directly using the hardware like 30 years before. A driver or dedicated application can allow multiple clients (browser windows) to access the devices functionality. A driver directly embedded in a web page can't. A driver in the webpage even means that once you close that page the communication state between PC and USB device is in any state (can't see a way for automatically doing anything meaningful on goaway), so the only thing that could be done is disconnect and reconnect the device. So some further implications are: Multiple tabs for your web app are not possible. And even other stuff like Ctrl-R would not work as desired (disconnect device, reconnect device, wait, wait, wait, ...).
The WebUSB approach also limits each device to be connected and controlled by exactly one browser frame which makes it not very desirable for sensor and other input applications.